The present invention concerns a procedure for the manufacture of a prosthesis for an extremity, principally an artificial leg of the kind that has for its attachment a sleeve which encloses the end of the remaining part of the extremity.
In the manufacture of prostheses, principally artificial legs, a positive model of that part of the extremity that remains, and which is to serve for the attachment of the artificial leg itself, is produced. In the normal course of events this model is made of a material like plaster, for example. Starting from this positive model a sleeve is then formed from a piece of thick sheet thermoplastic material which shall have as good contact as possible with the extremity. In practice, the formation of this sleeve is done is such a way that the sheet of material, which can have a thickness of about 25 mm, is heated in an oven until it becomes plastic, after which it is formed around the model, preferably by hand. This is an extremely laborious job which both takes a long time and also runs the risk of failure, among other things because the wall thickness of the finished sleeve will vary to a degree that cannot be accepted on account of the large deformations that are necessary, and furthermore in certain cases runs the risk of being so small that holes or perforations in or at the end of the sleeve can easily appear. If such a situation arises the work must be recommenced, since the sleeve cannot be repaired. In addition the forming of the heated plastic material over the model in this manner means that the surface structure of the plastic material, which in the beginning was smooth, will be damaged, for which reason it is impossible to manufacture a sleeve which is transparent over the whole or the major part of its surface even if a perfectly clear plastic material should be used.
When the sleeve has been completed in this manner, the furthermost end is provided with a check valve so that air can be released from the sleeve but not into it, and by this means the sleeve is firmly attached by suction to the end of the amputated extremity. Furthermore, using all available means, the shape of the sleeve must be checked in such a way, and if necessary so adjusted, that total contact exists if possible between the inside of the sleeve and the end of the amputated extremity. In addition the sleeve must be adapted to the shape of the extremity so that the surface pressure on the extremity will if possible be uniform.
This individual fitting of the sleeve is extremely troublesome since the patient has a very bad idea of where the pressure is too great, or where there is no surface contact at all. From this it follows that this individual fitting is very time-consuming and that there exists no guarantee that the result will be good.
It is also possible, and occurs in certain cases, that X-ray is used in the individual fitting of the sleeve. This method is however expensive and also to a certain extent time-consuming, and furthermore it can also be debatable for the reason that radiation doses that are repeated too often and of too high an intensity can be injurious.
When the sleeve has been adapted to the shape of the amputated extremity as well as it can be done the sleeve is subsequently built into the artificial limb itself and serves as its attachment to the extremity and its maneuvering. In a practical case, when an artifical leg is concerned, the sleeve can therefore have a diameter at the further end of magnitude 10-15 cm, while the diameter at the nearer end can be somewhat larger, and the length of magnitude 40 cm.
As has been indicated above, the familiar technique has quite a number of disadvantages. First of all, the essentially manual manufacture of the sleeve means both a high consumption of time and a great risk of failure or at any rate a less good result, depending amongh other things upon irregularities in the wall thickness of the sleeve, or in damage to the surface structure of the sleeve, or even upon the formation of creases in the sleeve material. Furthermore, the methods that are used for the individual fitting of the sleeve are quite inadequate since they are time-consuming and do not lead to a sure result.